DC/DC converter which ensures damping of voltage overshoots of a semiconductor switch

Abstract

A DC/DC converter has an active energy store, such as an inductance, which can be periodically charged and discharged by one or more semiconductor switches, such as transistors. To avoid voltage overshoot, an RCD element is provided for at least one semiconductor switch, wherein a capacitor and a diode of the RCD element are connected in series, and a resistor of the RCD element can be connected either in parallel with the diode or disconnected from the diode by a switch. The diode of the RCD element is arranged so as to be blocking in the conducting direction of the semiconductor switch.

What is claimed is: 
     
       1. A DC/DC converter, comprising
 an active energy store having an inductance, 
 a first controllable semiconductor switch configured to periodically charge the active energy store, and 
 a second controllable semiconductor switch configured to periodically discharge the active energy store, with at least one of the first and second controllable semiconductor switches having an RCD element to prevent voltage overshoots for the at least one of the first and second controllable semiconductor switches, said RCD element comprising a capacitor and a diode connected in series and a resistor, and furthermore a switch having a first switching position connecting the resistor in parallel with the diode and a second switching position disconnecting the resistor from the diode, wherein the diode is arranged in series with the capacitor so as to be conducting in a direction of a current flowing from an emitter to a collector of the at least one of the first and second controllable semiconductor switches and to be blocking the current when the at least one of the first and second controllable semiconductor switches is conducting. 
 
     
     
       2. The DC/DC converter of  claim 1 , wherein the resistor is connected in parallel to the capacitor in the second switching position. 
     
     
       3. The DC/DC converter of  claim 1 , wherein the RCD element is connected in parallel with the first controllable semiconductor switch. 
     
     
       4. The DC/DC converter of  claim 1 , wherein the RCD element is connected in parallel with the second controllable semiconductor switch. 
     
     
       5. The DC/DC converter of  claim 1 , wherein the RCD element is connected in parallel with a freewheeling diode. 
     
     
       6. The DC/DC converter of  claim 1 , wherein the switch is constructed as a relay. 
     
     
       7. The DC/DC converter of  claim 1 , wherein the switch is constructed as a transistor. 
     
     
       8. The DC/DC converter of  claim 1 , further comprising a charging circuit for charging the capacitor of the RCD element. 
     
     
       9. The DC/DC converter of  claim 1 , wherein the first controllable semiconductor switch comprises a first RCD element having a first diode and a first capacitor and the second controllable semiconductor switch comprises a second RCD element having a second diode and a second capacitor, with the first RCD element and the second RCD element having a shared resistor connected to a shared switch which connects the shared resistor in a first switching position in parallel with the first diode and in a second switching position in parallel with the second diode. 
     
     
       10. The DC/DC converter of  claim 1 , wherein the first controllable semiconductor switch comprises a buck converter transistor. 
     
     
       11. The DC/DC converter of  claim 1 , wherein the second controllable semiconductor switch comprises a step-up converter transistor. 
     
     
       12. The DC/DC converter of  claim 1 , wherein the first and second controllable semiconductor switches comprise transistors. 
     
     
       13. A method for operating a DC/DC converter having an active energy store in form of an inductance, a first controllable semiconductor switch constructed as a buck converter transistor configured to periodically charge the active energy store and a second controllable semiconductor switch constructed as a step-up converter transistor configured to periodically discharge the active energy store, with at least one of the first and second controllable semiconductor switches having an RCD element to prevent voltage overshoots for the at least one of the first and second controllable semiconductor switches, said RCD element comprising a capacitor and a diode connected in series and a resistor, and furthermore a switch having a first switching position connecting the resistor in parallel with the diode and a second switching position disconnecting the resistor from the diode, wherein the diode is arranged in series with the capacitor so as to be conducting in a direction of a current flowing from an emitter to a collector of the at least one of the first and second controllable semiconductor switches and to be blocking the current when the at least one of the first and second controllable semiconductor switches is conducting, the method comprising:
 for operation as a buck converter, switching only the buck converter transistor on, connecting the resistor in the RCD element, that is connected in parallel to the buck converter transistor, in parallel with the capacitor of the buck converter transistor, and 
 selectively connecting the resistor, that is connected in parallel with the step-up converter transistor, in parallel with the diode in the RCD element of the step-up converter transistor or disconnecting the resistor from the diode. 
 
     
     
       14. A method for operating a DC/DC converter having an active energy store in form of an inductance, a first controllable semiconductor switch constructed as a buck converter transistor configured to periodically charge the active energy store and a second controllable semiconductor switch constructed as a step-up converter transistor configured to periodically discharge the active energy store, with at least one of the first and second controllable semiconductor switches having an RCD element to prevent voltage overshoots for the at least one of the first and second controllable semiconductor switches, said RCD element comprising a capacitor and a diode connected in series and a resistor, and furthermore a switch having a first switching position connecting the resistor in parallel with the diode and a second switching position disconnecting the resistor from the diode, wherein the diode is arranged in series with the capacitor so as to be conducting in a direction of a current flowing from an emitter to a collector of the at least one of the first and second controllable semiconductor switches and to be blocking the current when the at least one of the first and second controllable semiconductor switches is conducting, the method comprising:
 for operation as a step-up converter, switching only the step-up converter transistor on, connecting the resistor in the RCD element, that is connected in parallel to the step-up converter transistor, in parallel with the capacitor of the step-up converter transistor, and 
 selectively connecting the resistor, that is connected in parallel with the buck converter transistor, in parallel with the diode in the RCD element of the buck converter transistor or disconnecting the resistor from the diode.